Disruption of the anterior cruciate ligament (ACL) is a common injury that usually requires surgical reconstruction to restore function and prevent the progression of post-traumatic osteoarthritis (OA). However, the procedure frequently produces degenerative changes with time. The initial tension applied to the graft at the time of surgery controls knee motion and the distribution of joint contact stress, factors thought to promote OA. Our primary objective is to evaluate the effects of initial graft tension on the articular cartilage response following ACL reconstruction in a prospective, randomized, double-blinded controlled study. Patients who are candidates for ACL reconstruction using patellar tendon grafts will be randomized into one of two treatment groups: 1) initial graft tension set such that the anterior-posterior (A-P) laxity of the reconstructed knee is equal to that of the contralateral normal knee (the "low-tension" treatment), and 2) initial graft tension set to reduce A-P laxity by 2-mm relative to that of the contralateral knee (the "high-tension" treatment). An additional group of subjects without evidence of knee injury will serve as a control. Objective measurement of joint space narrowing is the only validated measure for quantifying OA progression, and will serve as the primary outcome measure for the study. The effects of initial graft tension will also be assessed using the secondary outcome measures of A-P laxity (an indicator of graft integrity and knee kinematics), isokinetic strength (an indicator of dynamic function), and validated patient-oriented and clinical outcome scores. We hypothesize that after 3-years of healing, the temporal changes in the tibiofemoral joint space width (e.g. joint space narrowing) in the reconstructed knees of the "high-tension" treatment group will be equal to those of the control group, while the changes in the "low-tension" treatment group will be greater than those of the control group. The primary and secondary outcomes will allow us to perform a comprehensive evaluation of the effects of initial graft tension on ACL reconstruction. We will also explore the relationships between joint space narrowing and the secondary outcome measures to gain insight into possible mechanisms of OA progression. 54 subjects will serve in each experimental group and they will be followed for a minimum of 3-years.